An organic EL element has been actively researched and developed. In the fundamental structure of the organic EL element, a layer containing a light-emitting organic compound is interposed between a pair of electrodes. By applying voltage to this element, light emission from the light-emitting organic compound can be obtained.
The organic EL element can be formed into a film shape; thus, a large-area element can easily be formed. Therefore, the organic EL element has a high utility value as a surface light source that can be applied to lighting or the like.
For example, a lighting device including an organic EL element is disclosed in Patent Document 1.
Further, a display device in which an organic EL element and a thin film transistor are combined has been actively developed. A display device including an organic EL element does not need a backlight which is necessary for a liquid crystal display device, so that a reduction in thickness and an increase in luminance and contrast can be achieved.
As for an organic EL element, there are a bottom emission type in which light emission is extracted to a lower electrode layer side, a top emission type in which light emission is extracted to an upper electrode layer side, and a dual emission type in which light emission is extracted to a lower electrode layer side and an upper electrode layer side.